ORIGIN AND DEVELOPMENT OF ORE DEPOSITS. 



141 



ancient region ; yet, if we study the directions of the separate 

 " elements" of the lodes rather than their mean directions, the 

 fissures or parts belonging to each of the systems will generally 

 be recognizable, and often with great distinctness. 



That the fissures in any given region are really of various 

 ages is evident, since we find some clearly traversing others. 

 When the rocks are distinctly faulted this is still more evident, 

 yet we cannot always say with certainty that the latest fault 

 movement has taken place in the latest formed fissure. A study 

 of lode fillings teaches us that many fissures have been re-opened 

 again and again, and at widely different periods, and it is only 

 by a close study of the conditions of these fillings that we are 

 able to arrive in many cases at just conclusions hereon. This 

 branch of the subject will be further dealt with hereafter. 



Complex fissures. As then the movements of the ground in 

 an already fractured district could hardly ever be confined to 

 the production of new fissures, and as those old ones which 

 became re-opened would only be re-opened in some portions of 

 their course, it is easy to see that many complex fissures would 

 be likely to be formed capable of greatly misleading the super- 

 ficial observer. It will readily be understood that such complex 

 fissures are most likely to be formed when the angles between 

 the two systems are small. Thus the Cudna Reeth Lode at 

 Botallack mine appears to be heaved 20 fathoms to the right by 

 the Wheal Hazard lode, when the two are seen in plan, from 

 which fact we might conclude that it is the older of the two. It 

 appears, however, that the mineral deposit known as the Cudna 

 Reeth Lode, may be traced continuously through that of the 

 Wheal Hazard Lode, hence this at least is newer than the 

 Wheal Hazard Lode. A careful consideration of all the facts 

 observable leads to the following conclusions : — 



1st. — The Cudna Reeth fissure, with probably part of its 

 filling, was first formed. 



2nd. — The Wheal Hazard fissure was then formed and 

 subsequently filled, the Cudna Reeth Lode being heaved 20 

 fathoms. 



3rd. — A complex fissure consisting of the two portions of 

 the Cudna Reeth Lode with 20 fathoms of Wheel Hazard Lode 

 was opened up. 



